Charles D. Baker, the GOP’s defeated 2010 candidate, will announce a second gubernatorial campaign Wednesday, a much anticipated move that party insiders see as critical to Republican hopes of recapturing the governor’s office, according to three top Massachusetts Republican leaders briefed on his decision.

Baker, who held top cabinet posts in the Weld and Cellucci administrations, plans to roll out his candidacy for the 2014 election in a video to be released at 10am Wednesday. Baker will not hold a media availability until Thursday, but his political mentor, former governor William F. Weld, is expected to to speak to reporters sometime Wednesday.

Baker did not respond to calls seeking comment about his pending announcement.

His decision to run is hugely important in shaping the emerging race for governor that already has five Democrats seeking their party’s nomination.

Without Baker, the GOP would have been looking at a thin bench of viable candidates. Former US Senator Scott Brown’s recent announcement that he would not run for the office highlighted the party’s heavy reliance on Baker getting into the race.

Baker, 56, had long been considered a rising star in the Massachusetts political and government world, but his 2010 race to unseat Governor Deval L. Patrick scarred his image as a bipartisan moderate who could appeal to centrist independents and Democrats.

The post-election analysis laid much of the blame for his poor showing on his often strident appeals to the conservative right. One of Baker’s strong points should be the potential support he can get from across party lines and from moderate independents because of progressive positions on social, human services, and environmental issues.

But faced during the 2010 race with then state Treasurer Timothy P. Cahill, a former Democrat, running as an independent with appeals to the conservative Democrats and independents, Baker spent much of his effort covering his right flank. In the end, Patrick won re-election with 48 percent of the vote. Baker received 42 percent and Cahill got 8 percent.

Like Weld, he is an advocate of conservative fiscal policies with liberal social views. But he has acknowledged that he lacks Weld’s easygoing charm, and sometimes struggles to connect with workaday voters.

Democratic and Republican analysts said that Baker’s chances of winning will depend on his modulating the hard-edged image he projected in his first run.

Indeed, indications point to a Baker -- with some counseling from his political mentor Weld -- who is ready to run a far different campaign. For example, those familiar with his thinking said he will not sign a no-new-tax pledge as he did in 2010. He will also push hard on issues important to female voters, a bloc that voted heavily against him.

“It’s going to be a very different Charlie Baker,’’ said former state Senator Warren Tolman, one time Democratic candidate for governor. “He is a likeable guy. If he shows that, he will be very formidable.’’

Richard Tisei, the former senate minority leader who ran for lieutenant governor on the GOP’s 2010 ticket, said Baker has absorbed the lessons of his failed candidate and will now run a more effective race, one that allows his true personality to come through.

“Charlie realizes during the first time, voters didn’t get a good feel for who is and what he is all about,’’ said Tisei, noting Baker’s reputation both for a deep grasp of public policy and his affable personality, even among some of his strongest opponents. “It’s just a question of letting Charlie be Charlie. He doesn’t need to be packaged, he just needs to be himself.’’

Baker got his start in politics in the early 1980s, as a spokesman for the Massachusetts High Tech Council, a business lobby. He then joined the Pioneer Institute, a conservative think tank. Weld hired Baker into his new administration in 1991, and the young policy aide quickly moved up the ranks, serving as health and human services secretary and then administration and finance secretary, in charge of the state budget. Within the administration, he had a reputation as a boy wonder, with a penchant for holding long staff meetings on subjects ranging from tax reform to special education.

During that time, he was also an architect of the Big Dig financing plan, a fact that came back to haunt his 2010 run for governor when it became a main target of attack by Patrick. Baker left the State House in 1998 to lead Harvard Vanguard Medical Associates. He then spent 10 years as chief executive of Harvard Pilgrim Health Care, and was credited with helping to rescue the company from the edge of financial ruin. He remained involved in politics, though on a much smaller scale, as a selectman in his hometown of Swampscott.

After the 2010 election, he joined General Catalyst Partners, a venture capital firm in Cambridge. His work there has kept him out of the public eye, but it included a well-publicized $17 million equity financing deal for Oceans Healthcare, Louisiana’s largest provider of psychiatric facilities for geriatric patients. As part of the deal, Baker became chairman of the company’s board.

Baker, who grew up in Needham, comes from a politically involved family. His mother was a liberal Democrat and his father, Charles D. Baker, served as undersecretary of health and human services in the Reagan administration and as undersecretary of transportation during the Nixon years. He has remarked that family dinners first exposed him to intense political debates.

Baker played basketball at Harvard, and graduated with a degree in English in 1979. In 1986, he earned a master’s degree in business administration from the Kellogg School of Management at Northwestern University. He is married and a father of three.